The Development of World-Class High Rates, High Ultimate Recovery Wells in Deepwater Turbidites--Bonga Field, Offshore Nigeria

Abstract

fax 01-972-952-9435. AbstractBonga field in deepwater Nigeria produces hydrocarbons from classic deepwater turbidites reservoirs in channel settings. The reservoirs consist of series of amalgamated channel complexes with varying degrees of compartmentalization. This configuration presents significant uncertainties in connected volumes, well placements and sweep efficiency between water injector/producer well pairs. However, due to the high costs of deepwater developments, well count needs to be as low as practical, and production rates must be sustainably high to ensure economic robustness of the project. High rates and high ultimate recoveries are the foundations of successful deepwater projects, where constant pressure maintenance is a key component. Several research studies conducted recommended that water injection wells be designed for fractured injection in order to sustain the required high rates as opposed to matrix injection. This paper presents the results of these research efforts leading to this conclusion and the implications on reservoir management. Also presented is an overview of the challenges of developing these complex channel deposits as well as the new approach to modeling of high rate wells in deepwater turbidites.Key to a successful understanding of reservoir behaviour (connectivity) and early indications of future reservoir performance is through a systematic undertaking of interference tests at production start-up. After about 2 years of production, the results from the Bonga wells demonstrate that sustained high oil rates could be achieved with adequate pressure maintenance. Average oil production rates of vertical/deviated wells range between 15,000 to 22,000 bopd and that of horizontal wells range between 25,000 to 35,000 bopd. Estimated Ultimate recovery (EUR) range from 20 to 100 mmstb for phase 1wells and from 10 to 30 mmstb for phase 11 development wells with several opportunities for infill drilling of low EUR wells. Nameplate capacity of 225,000 bopd is achieved and sustained with just 9 producers and 6 injectors. In order to maintain reservoir pressures from these high uplift rates, world-class water injection rates of between 40,000 to 70,000 bbls per day per well have been sustained since first oil.The fracture injection approach is applicable both for onshore and offshore reservoir development but more significantly for deepwater reservoir development where sustained high rates and economic considerations are paramount.